1. Field of the Invention
This invention relates to a method of determining the failure of sensors in a control device for an internal combustion engine to prevent an erroneous determination when an electric power is activated.
2. Discussion of the Background
FIG. 2 is a constitution diagram showing a general control device for an internal combustion engine.
In this drawing, a numeral 1 designates a cylinder which drives an internal combustion engine, 2, an electromagnetic drive type injector (fuel injection valve) which supplies fuel, 3, an intake pipe which supplies air to the cylinder 1, 4, a hot wire type air-flow sensor which detects an air quantity sucked into the cylinder 1, 5, and intake air throttle valve which controls the air quantity sucked into the cylinder 1, 6, and exhaust pipe which discharges exhaust gas from the cylinder 1, and 7, a water temperature sensor which detects a temperature of the cylinder 8 based on that of cooling water.
The injector 2, the air flow sensor 4, the intake air throttle valve 5, and the water temperature sensor 7, are respectively disposed at the intake pipe 3. The injector 2 and the water temperature sensor 7 are disposed adjacent to the cylinder 1.
A numeral 8 designates a control device which controls, for instance, fuel injection quantity or the like based on signals from various sensors, which is equipped with an input interface 80 which receives signals, a microprocessor 81 which performs a calculation of input signals, a ROM 82 which stores a calculation program or the like, a RAM 83 which temporarily memorizes data in calculation, and an output interface 84 which outputs a control signal B or the like based on a calculation result.
A numeral 9 is an ignition device which ignites the cylinder 1 at a predetermined rotation angle, which also functions as a rotation sensor of the internal combustion engine, and which outputs an electric pulse corresponding to a rotation signal at every predetermined rotation angle as a pulse signal P.
The opening degree signal C from the intake air throttle valve 5 and the temperature signal D from the water temperature sensor 7 are inputted to the control device 8 with output signals from other sensors, not shown.
Next, explanation will be given to a control operation of fuel injection of the control device for an internal combustion shown in FIG. 2.
In the hot wire type air-flow sensor 4, a hot wire is installed at an intake air passage, a supply current thereof is controlled by a feed back control so that a hot wire temperature is maintained at a constant value (for instance, 160.degree. C.), and the supply current value to the hot wire is converted to an electric voltage and is outputted as an air quantity signal A. Accordingly, when air flow quantity is large and the cooling effect thereof is large, since the supply current is large, the level of the air quantity signal A is also enhanced. On the contrary, when the air flow quantity is small and the cooling effect thereof is small, since the supply current is small, the level of the air quantity signal A is diminished.
The control device 8 calculates a fuel quantity to be supplied to the cylinder 1 based on the air quantity signal A from the air flow sensor 4. At this time, a rotation pulse frequency number, that is, a rotation number of the internal combustion engine, is obtained based on the pulse signal P from the ignition device, and the fuel quantity per revolution is calculated. Furthermore, synchronizing with the pulse signal P, the control signal B having a required pulse width corresponding to a required fuel quantity, is applied to the injector 2.
Furthermore, a required air fuel ratio of the internal combustion engine, is necessary to be set to a rich side when the temperature of the cylinder 1 is low. The control device 8 corrects to increase the pulse width of the control signal B which is applied to the injector 2, based on the temperature signal D from the water temperature sensor 7. Furthermore, the control device 8 detects an acceleration state of the internal combustion engine based on the opening degree signal C from the intake air throttle valve 5, and corrects to increase the air fuel ratio to the rich side in the acceleration time.
Furthermore, the control device 8 always checks whether signals from various sensors are in allowable ranges. The control device 8 determines that the sensors are out of order in case that those signals are out of the allowable ranges, and stops the usage of the abnormal sensors. For instance, an upper limit value and a lower limit value of each sensor are predetermined. A failure of a sensor is detected when the value of the output signal of the sensor is equal to, or more than the upper limit value, and when the value is equal to or less than lower limit value.
However, a value of an output signal of each sensor may not be stabilized just after an electric power source is activated and may show an abnormal value. Therefore the control device 8 may perform an erroneous determination of a failure of the sensor. Particularly, in case of the air-flow sensor 4, the hot wire is cool just after the electric power source is activated. The hot wire must be heated by the supply current. Before such warmup the air quantity signal A assumes an abnormal value above a normal one and the possibility of an erroneous determination of the failure of the sensor is increased. When an erroneous determination is made that a sensor is in failure, the control device 8 is in the state in which a normally functional sensor is not utilized, which lowers the reliability of the control device 8.
In the conventional method of determining a failure of a sensor in a control device for an internal engine, as stated above, the value of the output signal of the sensor is compared with an allowable range for determining a failure of the sensor. Therefore, there is a possibility of an erroneous determination of the failure by an abnormal operation of sensors when an electric power source is activated, which impairs the reliability of control.